1. Technical Field of the Invention
The present invention relates to the inspection of structures on an object and, more specifically, to a system and method for optically obtaining three-dimensional information regarding the position of structures on the surface of an object at high speeds.
2. Description of Related Art
Optical inspection devices typically hold an object to be inspected under an overhead camera, and illuminate the object from a single or multiple light sources. Typically, the optical inspection device lights the object from several directions in order to fully illuminate the surface and any objects thereon. The overhead camera captures a two-dimensional gray-scale (black-and-white) image of the object and structures. In a process commonly called convolution, this image is then sent to a computer which compares the image, pixel by pixel, to a stored image of an object with properly positioned structures thereon. If any differences between the captured image and the image of the object with properly positioned structures are detected, the computer has detected a defective object. A typical application of this inspection technology is in the inspection of printed circuit boards (PCBs).
Other techniques for optical inspection such as the generation of structure grammar from captured images, tracing of structures to produce a set of primitives for the structure edges, the use of alignment techniques utilizing histograms to compensate for vibration and wobble of the support mechanism, and methods of automatic defect classification are disclosed in co-owned U.S. Pat. No. 6,487,307 entitled System and Method of Optically Inspecting Structures on an Object, and co-owned U.S. Pat. No. 6,292,260 entitled System and Method of Optically Inspecting Surface Structures on an Object, both of which are hereby incorporated by reference herein in their entireties.
Existing optical inspection systems d methods are becoming very efficient at obtaining and analyzing surface structures and defects which reveal themselves in the two dimensions of the surface of the object. However, there is still a problem in rapidly and efficiently obtaining detailed and accurate information about the height of the structures. Some prior art systems have used lasers to obtain height information. When a laser is pointed at a particular point on the surface of the object, a small dot is formed by the laser beam. If the angle of incidence of the laser beam is less than 90 degrees, and there is a structure at this point, the dot is displaced horizontally from the position where the dot would be if there was no structure. The taller the structure, the greater the displacement. The vertically mounted camera can then detect the displacement of the laser dot, and height information can be computed from the magnitude of the displacement in a process known as triangular then. However, this is a slow and inefficient process which is not suitable for obtaining height information over the entire surface of the object.
In order to overcome the disadvantage of existing solutions, it would be advantageous to have a system and method of rapidly and efficiently obtaining three-dimensional information regarding the position of structures on the surface of an object. The present invention provides such a system and method.